The present invention relates to a technique for forming a liquid film by supplying a liquid onto a substrate to be processed, and more specifically, to an apparatus and method of selectively forming the liquid film on the substrate.
In a manufacturing step of the semiconductor device, a liquid such as a resist or an SOG (Spin on Glass) solution is coated on a substrate. In a spin-coating method which has been conventionally used in a lithographic process to coat the liquid on the substrate, almost all amount of the liquid supplied onto the substrate is discarded out of the substrate and the remainder (several %) held on the substrate is used in forming a film. Therefore, a large amount of the liquid (such as a chemical agent) is wasted. Furthermore, a large amount of the chemical agent is released outside, negatively affecting the environment. In the case where a rectangular substrate or a large-aperture disk-form substrate (12 inches or more) is used, a turbulence is generated around the substrate, with the result that the obtained film is not uniform at outer peripheral portion thereof.
As a method of coating the chemical agent uniformly over the main surface of a substrate while the chemical agent is not wasted, Japanese Patent Application KOKAI Publication No. 2-220428 discloses a method of forming a uniform film by supplying a resist from a plurality of nozzles arranged in line and then blowing a gas or a liquid to the film formation surface behind the resist. Japanese Patent Application KOKAI Publication No. 6-151295 discloses a method of forming a uniform film by spraying a resist to a substrate from a plurality of spray holes formed in a rod. Japanese Patent Application KOKAI Publication No. 7-321001 discloses a method of forming a uniform film by moving a spray head having numeral spray holes for spraying a resist relative to a substrate. All of the coating apparatuses mentioned are directed to the formation of a uniform film by moving output nozzles or spray nozzles arranged laterally in line in a scanning manner along a substrate surface.
To use the chemical agent without waste, a method has been proposed in which a liquid film is formed by supplying a liquid from a nozzle selectively to a film formation region of the substrate. As such a selective film formation method using a liquid supply nozzle, known is a method using an accurate coating nozzle (manufactured by EFD CO., Ltd.) in which output of the liquid can be controlled in an ON/OFF manner.
In the method using the accurate coating nozzle, a liquid 13 is shut out by driving a valve such as a needle 171 or a screw 181, which is provided within a nozzle positioned above an output port 172, as shown in FIGS. 1 and 2.
This system has a problematic phenomenon where particles are generated by friction between the valve and the liquid when the valve is driven, and the particles are delivered to the substrate by being contained in a liquid supplied dropwise onto the substrate when the valve is opened. This system has another problematic phenomenon where pressure applied to the liquid slightly changes immediately after the valve is opened and thereby a pulsation flow occurs. Due to the pulsation flow, the thickness of the formed film changes.
More specifically, if a liquid film is selectively formed on the substrate while controlling output of the liquid by operating the valve arranged before the output port, as described, a problem of liquid-film contamination with the particles comes up. In addition, if the pulsation flow occurs, the liquid film is formed non-uniformly in thickness.
If the substrate has an uneven surface due to various patterns formed thereon, the following problems come up.
As shown in FIG. 3, if constructs 102 are formed on a substrate 101 and the ratio of the depressed portion is different depending on regions of the substrate surface, the thickness of films 103a, 103b, and 103c differs. In this case, the surfaces of the films are not formed uniform. Then, if the structure shown in FIG. 3 is subjected to a reflow processing, the resultant films, for example, insulating films 104a, 104b, and 104c, can be flattened, as shown in FIG. 4A.
However, depending upon the difference in ratio of the depressed portion, the insulating films 104a, 104b, 104c differ in surface level (height). Therefore, when resist patterns 106a-106c are formed on the insulating films 104a-104c with an antireflection film 105 interposed between them and exposed to light, some of them are defocused. The resist patterns 106a-106c obtained after the light exposure have a problem in that line widths thereof drastically vary each other as shown in FIG. 4B.
In brief, as described, the spin-rotation method has a problem in that almost all amount of liquid supplied dropwise on the substrate is wasted. On the other hand, the method of supplying the liquid dropwise onto the substrate has a problem in that the formed liquid film differs in height (level) from the substrate depending upon projections and depressions of the pattern formed on the substrate. In other words, the formed liquid film is non-uniform in thickness measured from the substrate surface.